Numerical and Experimental Study on a Solar Water Heating System in Lhasa

Lhasa is a “solar city” with high altitude, located in a cold zone in China. Due to the lack of mineral energy sources and the fragility of its ecological environment, solar heating technology is the first choice to satisfy the demand of indoor thermal comfort for building heating. In this study, an accurate solar heating system in Lhasa was investigated under the simultaneous charging and discharging operation mode. Based on the solar heating system, a numerical calculation method of the tank temperature distribution under the simultaneous charging and discharging operation mode was proposed and validated by experiments. This numerical method offers a correlation between the output water temperatures of the tank and the input water temperatures of the tank, which can be used to optimize the thermal performance of the solar heating system in future studies. To evaluate the system performance under the simultaneous charging and discharging operation mode, the transient coefficient of performance (COP) of the heating system was calculated based on the experimental measurements. The calculated results showed that the system COP reached an average number of 3.0, which was nearly equal to that of gas-boiler heating system and much higher than that of electrical heating systems. A north-facing room and a south-facing room were both selected to test whether the room temperatures met the heating requirements. The test results showed that the north-facing room had an average temperature over 17 ◦C while the south-facing room was over 20 ◦C, which illustrated that a good heating effect was achieved. Although a relatively high system COP was shown with a good heating effect for the solar heating system under the simultaneous charging and discharging operation mode, further recommendations were proposed for the mass flow rates of the solar collecting cycles and control stagey of the fan coil unit (FCU).